Millions have been displaced and more than 130 people killed in Bangladesh, India, and Nepal as the onset of the 2019 South Asian monsoon triggers floods and landslides across South Asia. The floods in Bangladesh are possibly the worst in recent years. In Bangladesh, the Jamuna River broke through an embankment on the night of 17 July 2019, inundating at least 40 villages and displacing more than 200,000 peoples. Official estimates report that over 100,900 ha of crops have been damaged and livestock, fisheries, and poultry have been severely impacted by the floods in Bangladesh.
In view of the recent flooding events in South Asia, ICIMOD has prepared flood inundation maps by analysing freely available satellite imagery. These maps provide a synoptic overview of the extent of the inundation caused by the floods and can aid disaster management agencies in prioritizing relief and rescue activities in flood-affected areas. The maps have been prepared using Sentinel-1 satellite images made available by Copernicus – the Earth observation and monitoring system managed by the European Commission.
(Before/After) Sentinel-1 imagery from 25 June 2019 and 18 July 2019 provide a synoptic overview of the extent of the floods. The blue sections in the imagery indicates flood-inundated areas and perennial water bodies.
Experts at ICIMOD opted for spaceborne synthetic aperture radar systems to monitor flood conditions, primarily because they are independent of solar illumination and have a very low dependency on atmospheric conditions. The presence of cloud cover hinders analysis and interpretation using conventional optical sensors. A mosaic of multiples scenes – a single Sentinel-1 satellite image scene covers an area of 250 ×170 km2 – provides a bird’s eye view of the extent of the inundation across multiple districts in Bangladesh.
The inundation maps have been also made available as an interactive mapping application using ArcGIS Online, a cloud-based mapping platform hosted at ICIMOD. The web application will be regularly updated to include more inundation maps as more satellite imagery becomes available. Data used in the application will be made available for download from ICIMOD’s Regional Database System. Experts at ICIMOD are liaising with line agencies so that the generated information can be put to use. Processed datasets are being made available to relevant agencies on request.
(Before/After) Administrative boundaries overlaid over Sentinel-1 imagery from 25 June 2019 and 21 July 2019 show the extent of the floods in different districts in Bangladesh. The blue sections in the imagery indicates flood-inundated areas and perennial water bodies.
A similar exercise in 2017 mapped the extent of the floods in northern Bangladesh and India, and southern Nepal. The framework was further developed into an operational methodology for rapid mapping and appraisal of flood-inundated areas and potential flood-affected areas to support a quick and effective event response in Bangladesh. This process has been captured in a peer-reviewed open access article.
ICIMOD carried out this mapping activity as part of the rapid response mapping activities under the framework of the SERVIR Hindu Kush Himalaya (SERVIR-HKH) Initiative. ICIMOD hosts the SERVIR-HKH hub and is a part of a larger SERVIR network – a joint development initiative of the United States Agency for International Development (USAID) and the National Aeronautics and Space Administration (NASA).